The present invention relates to a method for texturing a magnetic disc, and more particularly to a method for efficiently and precisely polishing or texturing a surface of a substrate of a magnetic disc.
In recent years, magnetic recording media such as magnetic discs have been increasingly utilized as an external storage device in association with the development of information processing techniques such as computers.
Hitherto, as the magnetic recording media, there have been used those produced by subjecting an aluminum alloy substrate to an alumite treatment or plating the substrate with a non-magnetic material such as Ni--P, and then forming in turn a undercoat layer composed of Cr or the like, a magnetic thin film layer composed of Co-based alloy and a protective layer composed of a carbonaceous material on the substrate.
Further, in association with recent increasing demands for high capacity and high density of such magnetic recording media, the distance between a magnetic disc and a magnetic head, i.e., the flying height of the magnetic head from the surface of the magnetic disc has been required to be reduced to a value as low as 0.15 .mu.m or less. However, in the case where such an extremely small flying height of the magnetic head is used, when any unusual projections exist on the surface of the magnetic disc, there arises a risk that the magnetic head and the projections are contacted with each other, thereby causing a head crash and damaging the surface of the magnetic disc. Even when the projections are not so high as to undergo the head crash, the contact between the magnetic head and the projections is likely to cause various errors upon reading and writing of information.
On the other hand, miniaturization of the magnetic discs has been demanded in addition to the high capacity and high density. For this reason, a spindle motor or the other components used in a disc driving apparatus have also been required to be correspondingly miniaturized in size. This tends to cause the lack of motor torque, so that there arises such a phenomenon that the magnetic head is stuck and fixed on the surface of the magnetic disc, and therefore, cannot fly thereover. In order to prevent, the sticking of the magnetic head onto the surface of the magnetic disc by reducing the contact area therebetween, there have been used so-called "texturing", i.e., formation of fine traces or traces on the surface of the magnetic disc substrate.
Hitherto, as the methods of applying the texturing onto the surface of the magnetic disc substrate, there are known, for example, a tape abrasion method using a fixed grinding particle-type polishing tape (Japanese Patent. Application Laid-open (KOKAI) No. 1-86320(1989), etc.), a slurry abrasion method using a polishing tape to a surface of which a slurry containing polishing grains is applied (Japanese Patent Application Laid-open (KOKAI) No. 3-147518(1991), etc.), or the like.
However, in the case where the magnetic disc substrate is surface-treated by the texturing to such an extent as to satisfy both a flying property (low flying height, high flying stability, etc.) of the magnetic head and a high anti-wear property (i.e., reduction in surface roughness of the substrate and strengthening of the finishing treatment of the disc), the surface roughness of the substrate must be extremely reduced to meet the requirement of recent drastic increase in recording capacity and recording density of magnetic recording media.
That is, it has been required to achieve, with a high accuracy, extremely low surface roughness (Ra), for example, not more than 15 .ANG. and extremely low maximum projection height (Rp), for example, not more than 40 .ANG., by the texturing. Further, the texturing must be conducted with a high efficiency as well as the high accuracy.
However, in the afore-mentioned conventional texturing methods, it has been extremely difficult to conduct the texturing with such a high accuracy.
As a result of the present inventors' earnest studies to solve the afore-mentioned problems, it has been found that by bringing a specific tape into contact with a magnetic disc substrate in a slurry in which polishing grains are dispersed, there can be formed a textured surface of the magnetic disc substrate, which can exhibit a low surface roughness (Ra) and a low maximum projection height (Rp) with an excellent high accuracy. The present invention has been attained on the basis of this finding.